Network Working Group G. Bernstein Internet Draft Grotto Networking Intended status: Informational Y. Lee Expires: November 2009 Huawei Ben Mack-Crane Huawei May 21, 2009 WSON Signal Characteristics and Network Element Compatibility Constraints for GMPLS draft-bernstein-ccamp-wson-signal-00.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." 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Abstract While the current GMPLS WSON formalism can deal with many types of wavelength switching systems there is a desire to extend this control plane to include other common optical or hybrid electro optical systems such as OEO switches, regenerators, and wavelength converters. This document provides a WSON signal definition and characterization based on ITU-T interface and signal class standards and describes the signal compatibility constraints of this extended set of network elements. The signal characterization and network element compatibility constraints enable GMPLS routing and signaling to control these devices and PCE to compute optical light-paths subject to signal compatibility attributes. Table of Contents 1. Introduction and Requirements..................................3 1.1. Regenerators..............................................3 1.2. OEO Switches..............................................6 1.3. Wavelength Converters.....................................7 2. Describing Optical Signals in GMPLS............................8 2.1. Optical Interfaces........................................8 2.2. Optical Tributary Signals.................................8 2.3. Proposed GMPLS WSON Signal Definition.....................9 2.4. Implications for GMPLS Signaling and PCEP................10 3. Characterizing WSON Network Elements in GMPLS.................11 3.1. Proposed Link and Network Element (NE) Model Extensions..11 4. Security Considerations.......................................12 5. IANA Considerations...........................................12 6. Acknowledgments...............................................12 7. References....................................................13 7.1. Normative References.....................................13 7.2. Informative References...................................14 Author's Addresses...............................................14 Intellectual Property Statement..................................14 Disclaimer of Validity...........................................15 Bernstein and Lee Expires November 21, 2009 [Page 2] Internet-Draft Wavelength Switched Optical Networks May 2009 1. Introduction and Requirements While the current GMPLS WSON formalism can deal with many types of wavelength switching systems, these systems must be located within optical signal networks to provide useful services. Therefore there is a desire to extend this control plane to include other common optical or hybrid electro optical systems required to build a complete optical signal network. In particular at the March 2009 IETF meeting the working group expressed a desire to include OEO switches, regenerators, and wavelength converters within the WSON GMPLS extensions. In the following we will describe these devices and their properties. We then show that a combination of additional signal attributes and network element attributes can be used to accommodate these devices, relate these attributes to ITU-T recommendations and describe the implications for GMPLS signaling, PCEP, and the WSON information model [WSON-Info]. It turns out OEO switches, wavelength converters and regenerators all share a similar property: they can be more or less "transparent" to an "optical signal" depending on their functionality and/or implementation. Regenerators have been fairly well characterized in this regard so we start by describing their properties. Our approach to efficiently extend WSON GMPLS to networks that include regenerators, OEO switches and wavelength converters is to add attributes characterizing the WSON signal in line with ITU-T standards, and add attributes describing signal compatibility constraints to WSON network elements. This way the control plane signaling and path computation functions can ensure "signal" compatibility between source, sink and any links or network elements as part of path selection process, and configure devices appropriately via signaling as part of the connection provisioning process. This enables integration of a WSON into the operations of a signal network for which it provides connectivity instead of requiring the WSON to be separately managed and controlled. 1.1. Regenerators The various approaches to regeneration are discussed in ITU-T G.872 Annex A [G.872]. They map a number of functions into the so-called 1R, 2R and 3R categories of regenerators as summarized in Table 1 below: Bernstein and Lee Expires November 21, 2009 [Page 3] Internet-Draft Wavelength Switched Optical Networks May 2009 Table 1 Regenerator functionality mapped to general regenerator classes from [G.872]. --------------------------------------------------------------------- 1R | Equal amplification of all frequencies within the amplification | bandwidth. There is no restriction upon information formats. +----------------------------------------------------------------- | Amplification with different gain for frequencies within the | amplification bandwidth. This could be applied to both single- | channel and multi-channel systems. +----------------------------------------------------------------- | Dispersion compensation (phase distortion). This analogue | process can be applied in either single-channel or multi- | channel systems. --------------------------------------------------------------------- 2R | Any or all 1R functions. Noise suppression. +----------------------------------------------------------------- | Digital reshaping (Schmitt Trigger function) with no clock | recovery. This is applicable to individual channels and can be | used for different bit rates but is not transparent to line | coding (modulation). -------------------------------------------------------------------- 3R | Any or all 1R and 2R functions. Complete regeneration of the | pulse shape including clock recovery and retiming within | required jitter limits. -------------------------------------------------------------------- From the previous table we can see that 1R regenerators are generally independent of signal modulation format (also known as line coding), but may work over a limited range of wavelength/frequencies. We see that 2R regenerators are generally applicable to a single digital stream and are dependent upon modulation format (line coding) and to a lesser extent are limited to a range of bit rates (but not a specific bit rate). Finally, 3R regenerators apply to a single channel, are dependent upon the modulation format and generally sensitive to the bit rate of digital signal, i.e., either are designed to only handle a specific bit rate or need to be programmed to accept and regenerate a specific bit rate. In all these types of regenerators the digital bit stream(s) contained within the optical or electrical is/(are) not modified. In the most common usage of regenerators the digital bit stream may be slightly modified for performance monitoring and fault management purposes. SONET, SDH and G.709 all have a digital signal "envelope" designed to be used between "regenerators" (in this case 3R regenerators). In SONET this is known as the "section" signal, in SDH this is known as the "regenerator section" signal, in G.709 this is known as an OTUk (Optical Channel Transport Unit-k). These signals Bernstein and Lee Expires November 21, 2009 [Page 4] Internet-Draft Wavelength Switched Optical Networks May 2009 reserve a portion of their frame structure (known as overhead) for use by regenerators. The nature of this overhead is summarized in Table 2. Table 2. SONET, SDH, and G.709 regenerator related overhead. +-----------------------------------------------------------------+ |Function | SONET/SDH | G.709 OTUk | | | Regenerator | | | | Section | | |------------------+----------------------+-----------------------| |Signal | J0 (section | Trail Trace | |Identifier | trace) | Identifier (TTI) | |------------------+----------------------+-----------------------| |Performance | BIP-8 (B1) | BIP-8 (within SM) | |Monitoring | | | |------------------+----------------------+-----------------------| |Management | D1-D3 bytes | GCC0 (general | |Communications | | communications | | | | channel) | |------------------+----------------------+-----------------------| |Fault Management | A1, A2 framing | FAS (frame alignment | | | bytes | signal), BDI(backward| | | | defect indication)BEI| | | | (backward error | | | | indication) | +------------------+----------------------+-----------------------| |Forward Error | P1,Q1 bytes | OTUk FEC | |Correction (FEC) | | | +-----------------------------------------------------------------+ In the previous table we see support for frame alignment, signal identification, and FEC. What this table also shows by its omission is that no switching or multiplexing occurs at this layer. This is a significant simplification for the control plane since control plane standards require a multi-layer approach when there are multiple switching layers, but not for "layering" to provide the management functions of Table 2. That is, many existing technologies covered by GMPLS contain extra management related layers that are essentially ignored by the control plane (though not by the management plane!). Hence, the approach here is to include regenerators and other devices at the WSON layer unless they provide higher layer switching and then a multi-layer or multi-region approach [RFC5212] is called for. In a sense dependence on client signal type represents a fourth regenerator type, i.e., 4R, that includes all the capabilities and Bernstein and Lee Expires November 21, 2009 [Page 5] Internet-Draft Wavelength Switched Optical Networks May 2009 restrictions of a 3R, 2R, and 1R, and in addition is depending upon the format of the digital stream, i.e., these regenerators can accept only one type of stream or must be programmed to accommodate different stream types. Hence we see that depending upon the regenerator technology we may have the following constraints imposed by a regenerator device: List 1. Network Element Compatibility Constraints 1. Limited wavelength range (1R) -- Already modeled in GMPLS for WSON 2. Modulation type restriction (2R) 3. Bit rate range restriction (2R, 3R) 4. Exact bit rate restriction (3R) 5. Client signal dependence (4R) 1.2. OEO Switches A common place where optical-to-electrical-to-optical (OEO) processing may take place is in WSON switches that utilize (or contain) regenerators. A vendor may add regenerators to a switching system for a number of reasons. One obvious reason is to restore signal quality either before or after optical processing (switching). Another reason may be to convert the signal to an electronic form for switching then reconverting to an optical signal prior to egress from the switch. In this later case the regeneration is applied to adapt the signal to the switch fabric regardless of whether or not it is needed from a signal quality perspective. In either case these optical switches have the following signal processing restrictions that are essentially the same as those we described for regenerators in List 1. Note that a common system integration function in transport networks is to add multi-channel WDM interfaces to electro-optical switching systems such as G.709, SONET, SDH, IP, or Ethernet switching systems. Although such systems may have high layer switching functionality they, by their nature contain WSON functionality, though this maybe in the form of fixed WDM multiplexing and de-multiplexing functionality. See [WSON-FRAME] for how GMPLS WSON can model fixed devices. If they only contain higher layer (IP, Ethernet, SONET path, etc...) functionality then these systems act as a termination point Bernstein and Lee Expires November 21, 2009 [Page 6] Internet-Draft Wavelength Switched Optical Networks May 2009 for the WSON switching layer, otherwise they look like a combination of WSON end system and WSON switching system and could contain OEO conversions. Integrating WSON capabilities into electro-optical switching systems brings the WSON network into the operational domain of these systems and higher layer networks. By adding optical tributary attributes to the GMPLS control protocols this draft enables the integration of WSON subnetworks into the higher layer networks within which they reside and to which they provide flexible connectivity. This streamlines network operations by enabling a single request to establish a connection across both electro-optical and all optical elements within a higher layer network. The optical tributary attributes for a connection may be set based on the related attributes of the network element at the boundary of each new WSON subnetwork traversed by the connection. 1.3. Wavelength Converters In [WSON-FRAME] the motivation for utilizing wavelength converters was discussed. In essence a wavelength converter would take one or more optical channels on specific wavelengths and convert them to corresponding new specific wavelengths. Currently all optical wavelength converters exist but have not been widely deployed, hence the majority of wavelength converters are based on demodulation to an electrical signal and then re-modulation onto a new optical carrier, i.e., an OEO process. This process is very similar to that used for a regenerator except that the output optical wavelength will be different from the input optical wavelength. Hence in general wavelength converters have signal processing restrictions that are essentially the same as those we described for regenerators in List 1: (a) Limited input wavelength range (1R), Limited output wavelength range (b) Modulation type restriction (2R) (c) Bit rate range restriction (2R, 3R) (d) Exact bit rate restriction (3R) (e) Client signal dependence (4R) Bernstein and Lee Expires November 21, 2009 [Page 7] Internet-Draft Wavelength Switched Optical Networks May 2009 2. Describing Optical Signals in GMPLS In the previous section we saw that each of the additional network elements (OEO switches, regenerators, and wavelength converters) can impose constraints on the types of signals they can "process". Hence to enable the use of a larger set of network elements the first step is to define and characterize our "optical signal". 2.1. Optical Interfaces In wavelength switched optical networks (WSONs) our fundamental unit of switching is intuitively that of a "wavelength". The transmitters and receivers in these networks will deal with one wavelength at a time, while the switching systems themselves can deal with multiple wavelengths at a time. Hence we are generally concerned with multichannel dense wavelength division multiplexing (DWDM) networks with single channel interfaces. Interfaces of this type are defined in ITU-T recommendations [G.698.1] and [G.698.1]. Key non-impairment related parameters defined in [G.698.1] and [G.698.2] are: (a) Minimum Channel Spacing (GHz) (b) Bit-rate/Line coding of optical tributary signals (c) Minimum and Maximum central frequency We see that (a) and (c) above are related to properties of the link and have been modeled in [Otani],[WSON-FRAME], [WSON-Info] and (b) is related to the "signal". 2.2. Optical Tributary Signals The optical interface specifications [G.698.1], [G.698.2], and [G.959.1] all use the concept of an Optical Tributary Signal which is defined as "a single channel signal that is placed within an optical channel for transport across the optical network". Note the use of the qualifier "tributary" to indicate that this is a single channel entity and not a multichannel optical signal. This is our candidate terminology for the entity that we will be controlling in our GMPLS extensions for WSONs. There are a currently a number of different "flavors" of optical tributary signals, known as "optical tributary signal classes". These are currently characterized by a modulation format and bit rate range [G.959.1]: (a) optical tributary signal class NRZ 1.25G Bernstein and Lee Expires November 21, 2009 [Page 8] Internet-Draft Wavelength Switched Optical Networks May 2009 (b) optical tributary signal class NRZ 2.5G (c) optical tributary signal class NRZ 10G (d) optical tributary signal class NRZ 40G (e) optical tributary signal class RZ 40G Note that with advances in technology more optical tributary signal classes will be added and that this is currently an active area for standardization. Note that according to [G.698.2] it is important to fully specify the bit rate of the optical tributary signal: "When an optical system uses one of these codes, therefore, it is necessary to specify both the application code and also the exact bit rate of the system. In other words, there is no requirement for equipment compliant with one of these codes to operate over the complete range of bit rates specified for its optical tributary signal class." Hence we see that modulation format (optical tributary signal class) and bit rate are key in characterizing the optical tributary signal. 2.3. Proposed GMPLS WSON Signal Definition We proposed to call the signal that we will be working with an optical tributary signal like that defined in ITU-T G.698.1 and .2. This is an "entity" that can be put on an optical communications channel formed from links and network elements in a WSON. An optical tributary signal has the following attributes: List 2. Optical Tributary Signal Attributes 1. Optical tributary signal class: This relates to the specifics of modulation format, and bit rate range. Could possibly change along the path. For example when running through a 3R regenerator a different output modulation format could be used. This could be more prevalent if we are controlling combined metro and long haul networks. 2. FEC: Indicates whether forward error correction is used in the digital stream. Note that in [G.707] this is indicated in the signal itself via the FEC status indication (FSI) byte, while in Bernstein and Lee Expires November 21, 2009 [Page 9] Internet-Draft Wavelength Switched Optical Networks May 2009 [G.709] this can be inferred from whether the FEC field of the OTUk is all zeros or not. 3. Bit rate. This typically would not change since we are not changing the digital bit stream in any end-to-end meaningful way. 4. Center frequency (wavelength). Can change along path if there are wavelength converters. This is already modeled via labels in GMPLS. 5. G-PID: General Protocol Identifier for the information format. This would not change since this describes the encoded bit stream. This is already present in GMPLS signaling. A set of G-PID values are already defined for lambda switching in [RFC3471], [RFC4328]. 6. (Optional) A signal identifier or name distinguishing a particular tributary signal from others in the network that may be used to detect misconnection of signals. For example this can be used in setting up the section trace in SDH or the trail trace identifier in G.709 between format aware regenerators. This is not used in determining signal compatibility with network elements and hence is optional. These attributes are used during RWA to select a compatible path for the optical tributary signal. These attributes are used during signaling to configure devices such as wavelength converters or parameter sensitive devices such as 3R regenerators. Some of these attributes such as wavelength may change as the optical tributary signal traverses the path from source to sink. 2.4. Implications for GMPLS Signaling and PCEP When establishing a connection or requesting a path computation the attributes of the optical tributary signal given in List 2 in section 2.3. needs to be furnished. However of these five attributes two are already supplied in GMPLS signaling: wavelength and G-PID. This leaves only four new types of attributes: 1. Signal Class with possible qualifying parameters 2. Bit Rate 3. FEC information 4. Optional signal identifier For RSVP-TE signaling these could be put in a new WSON T_SPEC object. For PCEP these signal attributes would need to be included in various request and response messages. Bernstein and Lee Expires November 21, 2009 [Page 10] Internet-Draft Wavelength Switched Optical Networks May 2009 3. Characterizing WSON Network Elements in GMPLS A number of processes may operate on an "optical tributary signal" as it traverses a path through a network these include: Generation (including modulation), Regeneration, Wavelength Conversion, Switching and Reception (including demodulation). In any of these processes a number of attributes of the "optical tributary signal" may be either constrained or incompatible with those of the processing elements. These attributes include: (a) Optical tributary signal class (modulation format and approximate bit rate, FEC) (b) Exact bit rate (c) Center frequency (wavelength) (d) Digital stream format information Qualification of a route involves determining that the route provides a signal path capable of propagating the physical layer network signal and meeting the input signal requirements of the termination sink function (receiver). Some of the previously mentioned attributes of our optical tributary signal may change as the signal traverses its path across a network. The most common of these would be center frequency (wavelength). GMPLS signaling currently supports the specification of wavelength to be used at a given point on a path. Less common, although, possible would be a change in modulation format of the signal, particularly after some type of OEO regeneration or switching. Currently GMPLS signaling doesn't support indicating a change of modulation at a particular point in the network. The bulk of compatibility checking of network element capabilities against optical tributary signal attributes would fall on the path computation entity whose traffic engineering database is typically constructed with the help of a link state IGP. Currently, only layer type information is given in the form of the interface switching capability descriptor (ISCD) from [RFC4202]. 3.1. Proposed Link and Network Element (NE) Model Extensions Other drafts [WSON-FRAME],[WSON-Info] provide NE models that include switching asymmetry and port wavelength constraints here we add Bernstein and Lee Expires November 21, 2009 [Page 11] Internet-Draft Wavelength Switched Optical Networks May 2009 parameters to our existing node and link models to take into account restrictions on the optical tributary signal attributes that a network element can accept. These are: 1. Permitted optical tributary signal classes: A list of optical tributary signal classes that can be processed by this network element or carried over this link. 2. Acceptable Bit Rate Set: A list of specific bit rates or bit rate ranges that the device can accommodate. Coarse bit rate info is included with the optical tributary signal class restrictions. 3. Acceptable G-PID list: A list of G-PIDs corresponding to the "client" digital streams that are compatible with this device. Note that such parameters could be specified on an (a) Network element wide basis, (b) a per port basis, (c) on a per regenerator basis. Typically such information has been on a per port basis, e.g., the GMPLS interface switching capability descriptor [RFC4202]. However, in [WSON-FRAME] we give examples of shared wavelength converters within a switching system, and hence this would be on a subsystem basis. The exact form would be defined in the [WSON-Info] and [WSON-Encoding] drafts. 4. Security Considerations This document has no requirement for a change to the security models within GMPLS and associated protocols. That is the OSPF-TE, RSVP-TE, and PCEP [RFC5540] security models could be operated unchanged. Furthermore the additional information distributed in order to extend GMPLS capabilities to the additional network elements discussed in this document represents a disclosure of network capabilities that an operator may wish to keep private. Consideration should be given to securing this information. 5. IANA Considerations This document makes no request for IANA actions. 6. Acknowledgments This document was prepared using 2-Word-v2.0.template.dot. Bernstein and Lee Expires November 21, 2009 [Page 12] Internet-Draft Wavelength Switched Optical Networks May 2009 7. References 7.1. Normative References [RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description", RFC 3471, January 2003. [RFC4202] Kompella, K. and Y. Rekhter, "Routing Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4202, October 2005. [RFC4328] Papadimitriou, D., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Extensions for G.709 Optical Transport Networks Control", RFC 4328, January 2006. [G.694.1] ITU-T Recommendation G.694.1, "Spectral grids for WDM applications: DWDM frequency grid", June, 2002. [RFC5212] Shiomoto, K., Papadimitriou, D., Le Roux, JL., Vigoureux, M., and D. Brungard, "Requirements for GMPLS-Based Multi- Region and Multi-Layer Networks (MRN/MLN)", RFC 5212, July 2008. [RFC5540] J.P. Vasseur and J.L. Le Roux (Editors), "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5540, March 2009. [WSON-FRAME] Y. Lee, G. Bernstein, W. Imajuku, "Framework for GMPLS and PCE Control of Wavelength Switched Optical Networks (WSON)", draft-ietf-ccamp-rwa-wson-framework-02.txt, March 2009. [WSON-Info] Y. Lee, G. Bernstein, D. Li, W. Imajuku, "Routing and Wavelength Assignment Information for Wavelength Switched Optical Networks", draft-bernstein-ccamp-wson-info-03.txt, March, 2009. [WSON-Encoding] G. Bernstein, Y. Lee, D. Li, W. Imajuku, "Routing and Wavelength Assignment Information Encoding for Wavelength Switched Optical networks", work in progress, draft-ietf- ccamp-rwa-wson-encode-01.txt, March 2009. Bernstein and Lee Expires November 21, 2009 [Page 13] Internet-Draft Wavelength Switched Optical Networks May 2009 7.2. Informative References [Otani] T. Otani, H. Guo, K. Miyazaki, D. Caviglia, "Generalized Labels for G.694 Lambda-Switching Capable Label Switching Routers (LSR)", work in progress, draft-ietf-ccamp-gmpls-g- 694-lambda-labels-04.txt [G.872] ITU-T Recommendation G.872, Architecture of optical transport networks, November 2001. [G.959.1] ITU-T Recommendation G.959.1, Optical Transport Network Physical Layer Interfaces, March 2006. Author's Addresses Greg M. Bernstein Grotto Networking Fremont California, USA Phone: (510) 573-2237 Email: gregb@grotto-networking.com Young Lee Huawei Technologies 1700 Alma Drive, Suite 100 Plano, TX 75075 USA Phone: (972) 509-5599 (x2240) Email: ylee@huawei.com T. Benjamin Mack-Crane Huawei Technologies Downers Grove, Illinois Email: tmackcrane@huawei.com Intellectual Property Statement The IETF Trust takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in any IETF Document or the extent to which any license under such rights might or might not be available; nor does it Bernstein and Lee Expires November 21, 2009 [Page 14] Internet-Draft Wavelength Switched Optical Networks May 2009 represent that it has made any independent effort to identify any such rights. 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